The Ames test is a common method for checking for possible mutagenicity, and therefore potential carcinogenicity, of a compound. The test involves mutant S. typhimurium which cannot produce its own histidine. This strain must have media supplemented with histidine in order to grow.

In the test, mutant S. typhimurium are spread onto a plate with minimal histidine to support initial growth. The plate also contains active rat liver enzymes for results that more closely represent animal metabolic activities. A small disk filter is dipped in a solution of the test chemical and placed in the center of the plate. The test compound then leaches into the plate with higher concentrations of the compound toward the center, and very little or no compound near the outer rim. After 48 hours, bacteria will not grow if they have not undergone a reversion mutation to regain the ability to produce histidine. Those bacteria which have regained the ability to produce histidine will be able to synthesize their own histidine and will grow on the plate.

Safrole is a suspected weak carcinogen. It produces a positive Ames test and is a natural compound found in a variety of foods including cinnamon and basil. Safrole itself is not known to be carcinogenic, but two of its metabolites are. These are 1′-hydroxysafrole and 3′-hydroxysafrole, and are found in rat urine after being fed with safrole. These safrole metabolites are known to be carcinogens in humans.
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